1. Field of the Invention
The present invention relates to systems and methods for determining the amount of refrigerant in vapor compression systems, and more specifically to a device and method for determining such amount by measuring the refrigerant collected in a sight glass attached to the system.
2. Description of the Related Art
Heating, ventilating, air conditioning, and refrigeration systems rely on cycling a refrigerant through stages of compression and expansion. As the refrigerant undergoes compression, it changes state from a gas to a liquid. As the refrigerant expands, it reverts to the gas phase. The thermodynamic properties of the refrigerant are such that these phase changes produce certain desired conditioning effects, such as cooling, heating, and dehumidifying.
In order for these systems to operate optimally, the amount of refrigerant must be maintained at certain desired levels. If the refrigerant charge diminishes, as may happen in the case of a system leak, system performance may suffer. Thus, knowing the amount of refrigerant in a system at any given time provides helpful diagnostic information. Moreover, the ability to determine the amount of refrigerant allows a manufacturer or user to develop performance specifications based on empirical data obtained by observing how system performance values vary with differing amounts of refrigerant. For these and other reasons, there is a need to easily and economically determine the amount of refrigerant in an HVAC system at any given time.
Typically, if the amount of refrigerant in a vapor compression system is to be measured, all of the refrigerant must be removed from the system and then weighed. This procedure, apart from its time-consuming and labor-intensive nature, requires that the system be shut down for considerable time as the complete removal and subsequent recharging of the refrigerant takes place. Such downtime produces disadvantages, including, notably, the extended loss of conditioning to the environment served by the system.
While there are some devices and methods that provide for observing the refrigerant in a system without entirely evacuating the refrigerant, the approaches known to the inventors have drawbacks and/or fail to specifically determine the amount of refrigerant present in the system. For example, U.S. Pat. No. 3,191,397 to Kennedy is directed to an air conditioning system that includes means for determining whether the system contains the proper charge of refrigerant. This is accomplished by viewing the refrigerant through a sight glass disposed on a storage receptacle. If, during system operation, a liquid-vapor interface is observed, then the system contains the proper amount of refrigerant. This observation, though, fails to provide a quantitative measurement of the amount of refrigerant in the system, focusing instead on the quality of the refrigerant's phase. Thus, Kennedy provides but a threshold measurement--namely, whether an appropriate amount of refrigerant is present--rather than an actual volumetric measurement.